This invention lies in the field of fuel combustion apparatus. More particularly, it concerns the burning of fuels in furnaces. Still more particularly it concerns apparatus for sensing the pressure inside of the furnace, and causing an alarm whenever the furnace pressure exceeds atmospheric pressure.
In the process arts, where heat is released into a furnace to transfer to tube-contained fluids, it is common to rely on furnace "draft" for the induction of air which is required for fuel combustion. In such furnaces, it is harmful, and wasteful of fuel, when the pressure inside the furnace becomes greater than atmospheric pressure. In the normal terminology, a condition of "draft" means less than atmospheric pressure exists within the furnace. A condition of "pressure" means greater than atmospheric pressure within the furnace.
It is common at times for furnace pressure to exist without the knowledge of the furnace operators, and consequently fuel is lost, and furnace damage can occur, because the very hot furnace gases are forced outwardly through openings in the furnace structure. There is particular damage to the furnace roof, or more properly the furnace arch, where the greatest furnace pressure exists. Furnace draft increases with movement down the furnace, and decreases with movement up the furnace. Minimum draft at any point in the furnace and at any time, should be at least 0.03 W.C. Reference is made to Furnace Operations, by Reed, Gulf Publishing Company, page 84, Library of Congress card 72-84333.
Wind induced changes in atmospheric pressure far exceed 0.03 W.C. as they occur, and in the measurement of comparative furnace and atmospheric pressures, stabilization of atmospheric pressure is required. On page 93 of Furnace Operations there is shown means for piezometric stabilization of atmospheric pressure, as indicated by a gauge or manometer. The same device is required for atmospheric pressure stabilization for the indication of furnace pressure with the difference that, for pressure indication, there is gas movement, but in draft measurement there is no gas movement.